1. Technical Field
The presently disclosed subject matter relates to a mount structure for use in electric lamps, and more particularly to a mount structure for use in electric bulbs of the double-filament type for use in vehicular headlamps.
2. Description of the Related Art
FIG. 5 shows a lamp that includes a conventional mount structure for double filaments supported in a glass bulb. The lamp comprises an almost cylindrical glass bulb 50, which contains a filament serving as a high beam light-emitting source (high-beam filament) 51 and a filament serving as a low beam light-emitting source (low-beam filament) 52. These two filaments are arranged in parallel and almost in the same plane which is normal to the longitudinal direction of the glass bulb 50. The ends of the filaments 51, 52 are connected to and supported on two pairs of inner leads 51a, 51b and 52a, 52b. 
The inner leads 52a, 52b for supporting the low-beam filament 52 linearly extend a certain length from a bridge 53 in a direction substantially (exactly or almost) normal to the bridge 53 and have respective ends connected to ends of the low-beam filament 52.
On the other hand, the inner leads 51a, 51b for supporting the high-beam filament 51 are held at the bridge 53 inward from the pair of inner leads 52a, 52b. The inner leads 51a, 51b extend a certain length linearly from the bridge 53 in parallel with the inner leads 52a, 52b. They are then bent and extend a certain length linearly away from the bridge 53 outward (toward the positions of the inner leads 52a, 52b). They are bent again and extend a certain length linearly in parallel with the inner leads 52a, 52b. The ends of the inner leads 51a, 51b are connected to the ends of the high-beam filament 51.
As shown in FIG. 6, in a mount structure 56 configured as described above, the low-beam filament 52 and the pair of inner leads 52a, 52b for supporting the filament 52 are all located in a substantially horizontal reference plane H in the bulb 57. The high-beam filament 51 is located in a plane normal to the horizontal reference plane H and in parallel with the low-beam filament 52 and substantially in the same plane (see, for example, Japanese Patent Application No. JP 2006-147385A and its corresponding English translation, which are hereby incorporated in their entirety by reference).
Referring again to FIG. 5, in the above-configured mount structure 56, the light emitted from the low-beam filament 52 includes light L that is directed to a lower position (for example, towards the high-beam filament 51) than the horizontal reference plane H in the electric bulb 57. Part of the light L impinges on folded portions 58 of the inner leads 51a, 51b which support the high-beam filament 51. This part of the light L is then reflected in various directions from the folded portions 58.
Such reflected light (diffused light L) from the folded portions 58 transmits out of regular optical pathways to a reflector 60 having an inner reflecting surface and an outer lens 61 having appropriate lens-cuts for optical path control, as shown in FIG. 7. The reflector 60 and outer lend 61 are arranged to form a low-beam distribution pattern from the light emitted from the low-beam filament 52. Therefore, the reflected light from the high beam filament 51 is non-contributive to the formation of the low-beam distribution pattern, and may exert ill effects on the formation of the low-beam distribution pattern.
As shown in FIG. 8, there are a pair of outer leads 65a, 65b and a pair of outer leads 64a, 64b. They are connected to the pair of inner leads 52a, 52b for supporting the low-beam filament 52 and the pair of inner leads 51a, 51b for supporting the high-beam filament 51 in the electric bulb 57, respectively, and extend out of the glass bulb 50. These outer leads are connected to a common earth terminal (j), a low-beam filament terminal (i), and a high-beam filament terminal (h) arranged on a bulb base 62 in turn from one side. In this case, the outer lead 64a is electrically connected to the high-beam filament and is required to intersect the outer lead 65a which is electrically connected to the low-beam filament. In this case, it is possible for both to electrically contact each other at intersection (c) resulting in a short circuit.
The presently disclosed subject matter has been made in consideration of the above characteristics, features and problems and can be configured to provide a technology for a double-filament type lamp in which inner leads for supporting a high-beam filament are prevented from reflecting light emitted from a low-beam filament. This makes it possible to prevent unwanted occurrences of diffused light which do not contribute to formation of the low-beam distribution pattern but rather exerts ill effects. This is effective to form an optimal light distribution pattern.
The disclosed subject matter also includes a lamp that can be configured to prevent outer leads from intersecting and thus avoiding a possible electrical short-circuit when plural terminals are provided in a certain array on a tube base and are connected to the leads.